Chicago (/ʃɪˈkɑːɡoʊ/ (listen), locally also /-ˈkɔː-/), officially the City of Chicago, is the most populous city in Illinois, as well as the third most populous city in the United States. With an estimated population of 2,716,450 (2017), it is the most populous city in the Midwest. Chicago is the principal city of the Chicago metropolitan area, often referred to as Chicagoland, and the county seat of Cook County, the second most populous county in the United States. The metropolitan area, at nearly 10 million people, is the third-largest in the United States, and the fourth largest in North America (after Mexico City, New York City and Los Angeles) and the third largest metropolitan area in the world by land area.